How Much Onion is Toxic to Cats: Don’t Cross the Line

Cat owners see their feline friends as part of the family, so it’s only normal for them to try to give human foods to cats. Some foods are safe for felines, but what about onions? Is it safe? How much onion is toxic to cats, you might wonder.

Onion is an ingredient that’s widely found in many foods. It is present in pizza, soup, burger, coleslaw, flatbread, and even chicken curry. Thus, there’s a good chance that the food you’re considering giving to your pet has onion in it. But is it safe for cats to eat onion at all?

That’s the question that this article will answer. After reading this, you should have an idea on whether you should be giving onion to your cat at all, and if so, how much.

Is Onion Safe for Cats?

Onions are not at all safe for cats. In fact, it is considered poisonous to our feline friends.

Onions belong to the plant species called allium. This group also includes garlic, leeks, shallots, chives, and scallions.

Many members of the allium family are widely considered superfoods for us humans. Take garlic, for instance. It can lower blood pressure and fight colds and flu. Onions, meanwhile, can regulate blood sugar and promote good digestion.

But while alliums are highly regarded for their health benefits and culinary uses, they’re not exactly recommended for feline consumption. To put it bluntly, alliums like onion are considered to be poisonous to cats.

The chemical called n-propyl disulfide is the main cause of feline onion toxicity. This is an oxidant with a strong odor that gives both onion and garlic that distinctive aroma. It’s also the substance that causes eye irritation whenever an onion is sliced.

Unlike cats, humans can tolerate n-propyl disulfide. Our bodies are gifted with the enzyme that allows us to digest thiosulfate.

But our favorite furry friends, unfortunately, don’t have that ability. When they eat onions, the n-propyl sulfide will be absorbed through their gastrointestinal tracts before being converted into highly reactive oxidants.

If you remember your old science class, the red blood cells carry the hemoglobin protein which is responsible for transporting oxygen to various parts of the body. The highly reactive n-propyl sulfide oxidant that has been converted into oxidants will directly harm those red blood cells.

To be more specific, the exposed hemoglobin would form into sulfhemoglobin, which binds to the red blood cells and forms structures known as Heinz bodies. These structures, which can bind with special cells known as eccentrocytes, can make red blood cells more fragile. This can lead to blood cell rupture and impair the delivery of oxygen to the tissues.

Whew! That was a long explanation. The short version is: the oxidant from the onion will attach itself to the red blood cells in your cat’s body. Because the substance can’t be easily removed, the cat’s body will do the next easiest thing which is to destroy the red blood cells to get rid of the foreign substance.

When that happens, a condition called hemolytic anemia follows. It is an urgent medical condition that can lead to death if not treated by a veterinarian immediately.

Hemolytic anemia is not the only condition that can result from a cat ingesting onion. Anemia or low red blood cell count may also follow. In severe cases, anemia in cats may also result in organ damage, organ failure, and also death.

How Much Onion is Toxic to Cats?

Okay, we’ve been clear with the fact that onion is toxic for cats. But you may wonder: how much onion is poisonous to cats? Can you give just a small amount of onion to your pet like a slice of onion from your burger?

The answer: a big no.

Veterinarians say that 5g of onion for every 5 kilograms of body weight is harmful to cats. How big is that? To give you a better appreciation, a medium-sized onion already weighs 150 grams. Thus, a quarter-sliced onion would be enough to put your cat in the sick bay.

So let us just say there’s no need to measure—just don’t let your cat eat onion at all, even a tiny bit of it.

And that goes for all forms of onion, whether it is raw or cooked. Cooking onion won’t affect or reduce its toxicity to cats. Raw onion, including the bulb and the stem, should be kept away from cats. The same goes for onion powder since it is reported to have a higher toxicity rate than raw onion.

Aside from cats, dogs are also known to fall sick after ingesting onion, garlic, and other alliums. Canines, though, can resist the poisonous oxidant from onions better than cats. That’s because cats are obligate carnivores—generally speaking, they aren’t built to ingest vegetables at all, let alone onions. Other wildlife such as geese have also been reported to be prone to onion toxicity.

It’s a good thing that cats, with their inherent food pickiness, aren’t really attracted to onions, especially raw ones. You may wonder though: if cats are notorious for being choosy when it comes to food, why should you worry about your pet eating onion?

Well, raw onion has a pungent smell that cats won’t be able to stand. But cooked onion and leftover food containing this ingredient is a different case altogether. Cooked onion can be tasty and pleasant to cats especially those who are hungry. Don’t be surprised if a cat would open his mouth if you dangle a slice of onion from pizza, for instance.

What Happens to a Cat that Ingested Onions?

A cat that ingests onions will not only suffer from hemolytic anemia, or the breakdown of red blood cells. He may also suffer from panting. There will also be instances when the cat would show signs of weakness or lethargy.

Moreover, a cat who has ingested onion will have his appetite affected. He would hardly touch the food you give him. He may also vomit excessively. And there’s a good chance that he will have diarrhea, too.

Don’t expect any of these symptoms to become apparent an hour or so after a cat ingests onion. In most cases, it would take days for onion toxicity symptoms in cats to become noticeable. Signs of onion toxicosis in cats will become apparent in 10 to 12 hours, at the earliest.

If you suspect that your cat has eaten onions, don’t panic. Call your veterinarian right away. As you will learn later in this article, this condition can be treated, although you have to bring your pet to the vet at the first suspicion of onion poisoning.

Also, it would help your cat’s case if you can keep a sample of the food item that your pet ingested. You can also save the packaging, vial, or container as these may have all the information your veterinarian needs in assessing your pet’s condition.

How Can Cat with Hemolytic Anemia Be Treated?

Diagnosis of the cat will begin with a physical examination. The veterinarian will also review the feline’s medical history. In case you find yourself in such a situation, be ready to tell the veterinarian about your cat’s current diet.

The red blood cells of the cat will then be examined. The vet would need a small blood sample from the feline to confirm the presence of Heinz bodies on red blood cells. In some cases, the veterinarian may request a biochemistry profile to complete the diagnosis.

There’s no particular antidote or cure for onion toxicity in cats. As such, the feline will be treated with supportive care. He may be hospitalized so that intravenous fluid therapy can be administered to him. The fluid therapy will aim to flush the toxin out of his body, giving his body time to discontinue hemolyzing the red blood cells.

Treatment of onion toxicity can take days. Once the feline is stable, additional lab work such as blood examination and urine may be required by the veterinarian. This is to ensure that the cat’s body organs are functioning well.

Human Foods That Contain Onion

Obviously, foods that contain onions should never be given to cats. Just think of foods like pizza, flatbread, and burritos. The onion included in these foods can make your cat very sick when he ingests it. What other foodstuff should you keep away from your cat at all costs?

Here are some of the foods that contain onion and thus should be kept away from your cat:

Barbeque sauce

Tomato sauce

Potato salad

Tartar sauce

Burgers

Spinach soup

Corned beef

Onion rings

Certain hotdog styles/types like West Virginia Hot Dog

Gravy

Tacos

Nachos

Cheesesteaks

Panzanella

Salsa

Basmati Rice

If there’s a bit of good news about onion toxicity in cats, then it would have to be the fact that incidence rate is quite low. Only a handful calls on cat onion toxicity are recorded annually.

However, it is still critical for cat parents like you to be aware of onion toxicity in felines. This is especially relevant given that a recent study showed that cat owners are not well educated about pet toxins.

In the study, it was revealed that many cat parents don’t regard alliums like onion as toxic to their pets.

How to Keep Cats from Ingesting Onion

They say that prevention is better than cure. This also applies to cats and onions. So how do you ensure that your cat won’t accidentally ingest onion?

One way to prevent cats from eating onion is by not feeding them table scraps. There are many dishes that contain cooked onion and thus have the potential to cause harm to our favorite pets. While it can take a certain amount of onion to cause health problems to cats, it can be hard to gauge this when cats are fed with table scraps.

Also, don’t let your cat roam around your kitchen or table when you are preparing lunch or dinner or when cooking. As we’ve said earlier, onion is one of the more widely used ingredients, so there’s always the chance you have that on your counter or table. And while cats aren’t really known for grabbing food left on the table, it is better not to leave anything to chances. Simply keep the table and kitchen counters free from onions!

But what about food products that may contain onion or any other plants that belong to the allium family like garlic? While the chances of that happening are quite slim, you may want to check the product’s ingredient list. If onion or garlic is not among the first ten ingredients listed, then don’t worry as the product may be safe for cat consumption.

If there’s food containing onion powder which cats may be exposed to, then it would have to be baby food. While you may not offer baby food to your cat, there’s always the chance that your cat would reach for leftover baby food especially if he’s hungry. It would be a good idea to dispose of leftover baby food properly unless you want your cat to ingest it accidentally.

Finally, be more conscious of your cat’s whereabouts when you are cooking food with onion. Make sure he’s not loitering around the kitchen. Keep the onions in the fridge or in sealed drawers. If your pet like getting in your bins, make sure that the traces of onion are kept somewhere else.

Wrap Up

Like many members of the allium family, onion is healthy for humans but toxic to our cats. As little as 5g for every 5 kilograms of body weight is enough to cause cats to suffer from hemolytic anemia. It can lead to organ failure, damage, or death.

If your cat accidentally ate onion, we highly recommend you bring him to a veterinarian right away. Don’t wait for symptoms such as vomiting, lethargy, or diarrhea to happen. Immediate medical attention can spell the difference between life and death for a cat who ingested onion.

The bottom line is that onion is toxic to cats. Don’t let your cat eat even a slice of it. Did your cat accidentally ingest onion? Do you know anything else that cats aren’t supposed to eat? Please share any information you know in the comments section below; it could save lives.

If you want to cook delicious food for your cat, you can do so without onions. Find many delicious and healthy homemade cat food recipes here.

Martha Harvey is a skilled veterinarian and a member of American Veterinary Medical Association from Greeley, Colorado. She has 20 years experience of working in Animal Hospital. Martha loves all of her patients, but her favorite one is the Russian Blue cat Stitch, who lives with her.